Suppose the own price elasticity of demand for good X is -3, its income elasticity is 1, its advertising elasticity is 2, and the cross-price elasticity of demand between it and good Y is -4

(A) Consumption will increase 15%.

The own price elasticity is -3, meaning that elasticity is negative. This in turn means that when price increases, consumption will decline. Moreover, it means that consumption will decline by 3 percent for a one percent increase in price. So when the price of good X decreases by 5 percent, consumption will increase by 3*5 = 15%.

(B) Consumption will decrease by 24%.

The cross-price between good X and Y is -4, meaning again that elasticity is negative. Thus when the price of good Y increases, the consumption of good X will decline. In this problem, the consumption of good X will decline by 3 percent for a one percent increase in price of good Y. So when the price of good Y increases by 8 percent, consumption will decrease by 3*8 = 24%.

(C) Consumption will decrease by 8%.

The advertising elasticity is 4, which means that elasticity in this case is positive. Thus when the advertising expenditure decreases, we can assume that consumption will decrease. Specifically, consumption will decrease by 4 percent for a one percent decrease in advertising. So when advertising decreases by 4 percent, consumption will decrease by 2*4 = 8%.

(D) Consumption will increase by 1*4 = 4%.

The income elasticity here is 1, indicating that elasticity is positive. So when income increases, consumption will increase. Consumption here will increase by 1 percent for a one percent decrease in income, thus when income increases by 1 percent, consumption will increase by 1*4 = 4%.